1. Field of Invention
This invention relates to spring contacts for electrically contacting electronic devices. This invention further relates to methods of making the spring contacts.
2. Description of Related Art
Micro spring contacts have been used for various purposes in the semiconductor industry. For example, these contacts have been used for electrically connecting integrated circuits, or chips, to circuit boards and other devices using standard bonding techniques.
Spring contacts have also been used for establishing a temporary electrical contact between two devices.
Photolithographically patterned spring contacts are described in U.S. Pat. Nos. 5,613,861 and 5,848,685, each incorporated herein by reference in its entirety. The spring contacts are formed on substrates and electrically connect two devices. As shown in FIG. 1, a bonding structure 50 comprises a spring contact 60 composed of an elastic material. The spring contacts 60 can have an inherent stress gradient that causes a free portion 62 of the spring contact to bend up and away from a substrate 52. An anchor portion 64 of the spring contact 60 can be fixed to a substrate 52 and electrically connected to a first contact pad 20 on the substrate 52. The free portion 62 of the spring contact 60 includes a tip 66 that compliantly contacts a second contact pad 20 on a device 70.
FIG. 2 shows a probe card 32 including an array of the spring contacts 60. The spring contacts 60 which are aligned with contact pads 20 on the device 70 such that the spring contacts 60 compliantly contact the contact pads 20. The device 70 can then be tested or communicated with by a testing device electrically connected to the probe card 32.
Spring contacts can be used to test chips or integrated circuit devices. For example, probes including these spring contacts can be used for wafer-level and burn-in tests of devices. The spring contacts comprise spring metals and have a pointed tip at the free end of the spring contact. During testing, the spring contacts are brought into contact with the contact pads formed on chips or on various devices. The contacts pads are typically formed of aluminum. A native aluminum oxide naturally forms on the aluminum contact pads at room temperature. In order to make electrical contact with the aluminum contact pads, the pointed tip of the spring contacts must penetrate through the native oxide.
When the spring contacts are used in probe cards for testing integrated circuit devices, the tip is repeatedly brought into contact with the aluminum contact pads. To provide a desirable service life, these spring contacts should be able to withstand approximately 3xc3x97105 touchdowns (contacts) with different contact pads, each having a hard native oxide on the surface that is contacted by the spring contact tip. In order to meet this need, the tip must resist wear, which can blunt the tip and, consequently, reduce its ability to penetrate the native oxide film and make electrical contact with the contact pad during repeated probing. The tip should be a good electrical conductor to reduce the degradation of electrical contact resistance and be chemically passive with contact pad materials to reduce the galling of the tip with contact pad material. That is, to reduce galling effects, spring metal should have a low solubility of the contact pad metal.
U.S. Pat. No. 5,944,537, incorporated herein by reference in its entirety, discloses spring contacts including at least a portion that can comprise a wear resistant material. In embodiments of the spring contacts, the tip can be coated with a hard material to provide wear resistance.
This invention provides improved spring contacts.
This invention separately provides devices comprising the improved spring contacts that can be used for testing purposes.
This invention separately provides methods of making the spring contacts.
Exemplary embodiments of the spring contacts according to this invention comprise a free portion composed of a spring metal. The free portion includes side surfaces, a contact surface and a tip. A wear resistant material can be formed on the side surfaces and the contact surface. The wear resistant material can be any suitable material that provides the desired wear resistance properties.
In other exemplary embodiments of the spring contacts according to this invention, the wear resistant material can be formed on only a portion of the tip. The wear resistant material can be any suitable ceramic or metal material. For example, the wear resistant material can be a carbide formed at only a portion of the tip. In other embodiments, the wear resistant material can be formed on only a portion of the contact surface. For example, the wear resistant material can be formed as a strip.
In other exemplary embodiments of the spring contacts according to this invention, the wear resistant material can be formed between adjacent spring metal layers and at least partially exposed at the tip. The wear resistant material can be any suitable ceramic or metal material.
Exemplary embodiments of devices according to this invention can comprise a plurality of any of the above-described spring contacts according to this invention. For example, the devices can be probe cards. The probe cards can be used for various testing applications of chips and electronic devices.
This invention also provides methods of making the spring contacts. In embodiments, conventional coating and photolithographic techniques can be used to make the spring contacts.